The present invention relates to a method and apparatus for making an elongated cylindrical article from a billet of ductile metal and, more particularly, a method and apparatus for forming an electrical conductor. The electrical connector has a first cylindrical portion with a first outside diameter, the first cylindrical portion defining a first cylindrical recess therein, and a second cylindrical portion with a second outside diameter, the second cylindrical portion defining a second cylindrical recess therein. The second outside diameter is less than the first outside diameter.
The manufacture of articles of a ductile metal, such as copper or a copper alloy, has in the past been accomplished by various techniques, such as cold forming, machining, and extruding. U.S. Pat. No. 3,197,857, issued Aug. 3, 1965, to Nippert, discloses a method of making a cup-shaped housing of copper or copper alloy. A workpiece of copper material, having a weld ring brazed thereon, is placed in a confining die and subjected to pressure by a downwardly advancing male die portion, causing back-flow of the ductile metal along the outer surface of the tip of the male die portion. Subsequently, the workpiece is subjected to pressure by a compound male die which includes a central male die portion and an outer male die portion. The outer male die portion is forced against the workpiece to form a flange or rim in the cup-shaped housing by causing metal flow radially outward from the workpiece. The flow of ductile metal in the workpiece results in a finished part of the desired configuration being produced from the slug of copper metal without the necessity of machining, thereby eliminating the cost of machining operations and the accompanying material scrap loss.
U.S. Pat. No. 4,071,947, issued Feb. 7, 1978, to Nippert, discloses a method of making a bimetal resistance welding electrode. A bimetal slug or billet of copper alloy material and dispersion strengthened copper material is initially brazed together and, subsequently, a hollow cylindrical electrode shape is formed by means of a back-extrusion process in which a male extrusion punch is advanced downwardly into a containing die, causing the billet to extrude backward along the outside of the punch. While this type of extrusion process may be used to form an elongated cylindrical article having a central cylindrical recess or cavity, it should be noted that the lower surface of the extruded electrode in the Nippert '947 patent is substantially flat, and therefore permits the electrode to be ejected by a knockout punch.
A problem, however, develops where an elongated cylindrical article having both upper and lower cylindrical recesses is to be formed. If the lower cylindrical recess has a relatively large inside diameter such that the article wall thickness is relatively small, the bottom annular surface of the article presents little contact surface in the die for ejection of the extruded part by a knockout punch. Additionally, if the article wall is sufficiently thin, the wall may tend to buckle as the knockout punch is raised during ejection of the article from the die, thus ruining the extruded part.
Thus, it may be seen that there is a need for a method and apparatus for forming a thin walled cylindrical article defining a cylindrical recess, in which the article is forward extruded in a die and subsequently ejected successfully from the die without damage to the article.